We have continued to investigate potential pathogenic mechanisms associated with enteritis caused by the common pathogen Campylobacter jejuni. We have focused our attention on the ability of this organism to bind to and enter epithelial cells in vitro and have described the characteristics of this interaction. During the past year, we have demonstrated that C. jejuni can effectively translocate across polarized epithelial cell monolayers in a fashion similar to that of other enteroinvasive pathogens such as Salmonella typhimurium and that the translocation is dependent upon active bacterial protein synthesis. High resolution electrophoretic techniques have been used to characterize the number and nature of proteins that are synthesized by C. jejuni during interaction with epithelial cells. Other evidence indicates that these proteins are directly involved in facilitating the internalization of C. jejuni by epithelial cells. Antisera have been prepared which differentially react with C. jejuni cultured in the presence and absence of cells. These antisera have been used to identify recombinant clones in genomic libraries that produce novel C. jejuni proteins that are preferentially associated with bacteria cultured in the presence of epithelial cells. These latter studies should permit identification of essential C. jejuni virulence determinants.